1. Field of the Invention
The present invention relates to a piezoelectric resonant light-emitting-diode (LED) driving circuit, and in particular to a thin piezoelectric oscillator coupled with a single active switch to drive an LED.
2. The Prior Arts
With the rising price of oil, the ample supply of energy resources is a most important issue. Therefore, how to conserve energy and electricity is a critical task of the Industries. In this respect, lighting device occupying a very large proportion of energy consumption, has become an important item of energy conservation. Presently, the LED has been used widely as illumination device due to its advantages of high color saturation, mercury free, long service life, fast turn-on and turn-off speed, high illumination, low power consumption, light weight, thin profile, and compact size.
Presently, piezoelectric transformer is used mainly to drive an LED circuit. Wherein, voltage of AC power supply is rectified into DC voltage, then it goes through a full-bridge or half-bridge power amplifier to provide voltage of square wave. Then, a top-and-bottom symmetric pseudo-sine wave current is obtained for the square wave voltage through the resonance of an external inductor and input capacitance of a piezoelectric transformer, for inputting it into the piezoelectric transformer for voltage conversion. Finally, the AC current output by the piezoelectric transformer is rectified into a DC current by a rectifier to drive an LED. However, the design and disposition of a full-bridge circuit having four switches and a half-bridge circuit having double switches could increase cost and space occupied by the circuit. Also, the circuit design is rather complicated. Therefore, how to simplify the circuit design while achieving the same LED driving capability is a problem that has to be solved urgently.
Therefore, presently, the design and performance of the piezoelectric transformer LED driving circuit is not quite satisfactory, and it has much room for improvements.